In communications networks, the maximum transmission unit (MTU) of a communication protocol of a layer is the size (in bytes or octets) of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface. Standards can fix the size of an MTU; or systems may decide MTU at connect time. A larger MTU brings greater efficiency because each network packet carries more user data while protocol overheads remain fixed, resulting higher efficiency means an improvement in bulk protocol throughput. A larger MTU also means processing fewer packets for the same amount of data. In some systems, per-packet-processing can be a critical performance limitation. However, larger packets occupy a slow link for more time than a smaller packet, causing greater delays to subsequent packets, and increasing lad and minimum latency. For example, a 1500-byte packet, the largest allowed by Ethernet at the network layer, ties up a 14.4 k modem for about one second. Large packets are also problematic in the presence of communication errors. Corruption of a single bit in a packet requires that the entire packet be retransmitted. At a given bit error rate, larger packets are more likely to be corrupt.
In an IP network, the Internet Protocol works over many networking technologies, each of which may use packets of different size. While a host will know the MTU of its own interface and possibly that of its peers from initial handshakes, it will not initially know the lowest MTU in a chain of links to any other peers. Another problem is that higher-layer protocols may create packets larger than a particular link supports. To get around this issue, IPv4 allows fragmentation: dividing the datagram into pieces, each small enough to pass over the single link that is being fragmented for, using the MTU parameter configured for that interface. This fragmentation process takes place at the IP layer and marks packets it fragments so that the IP layer of the destination host knows it should reassemble the packets into the original datagram. This method, however, implies a number of possible drawbacks including increased overhead.
The Internet Protocol defines the Path MTU of an Internet transmission path as the smallest MTU of any of the IP hops of the path between a source and destination. The path MTU is the largest packet size that can traverse this path without suffering fragmentation. Path MTU discovery is a technique for determining the path MTU between two IP hosts. It works by setting the DF (Don't Fragment) option in the IP headers of outgoing packets. Any device along the path whose MTU is smaller than the packet will drop such packets and send back an ICMP “Destination Unreachable” message containing its MTU. This information allows the source host to reduce its assumed path MTU appropriately. The process repeats until the MTU becomes small enough to traverse the entire path without fragmentation.
The wireless cellular communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. With the optimization of the network design, many improvements have developed over various standards, especially in providing wireless IP services via an Evolved Packet System (EPS).
The EPS/IP bearer and connection management and allocation functionality can be provided towards the applications and the terminal devices using an Application Programming interface (API). For external applications, the EPS/IP bearer and connection management and allocation functionality may be provided through an AT command API in accordance with 3GPP TS 27.007 “AT command set for User Equipment (UE)”. AT commands are used for controlling Mobile Termination (MT) functions and GSM/UMTS network services from a Terminal Equipment (TE) through Terminal Adaptor (TA).
A solution is sought for controlling MTU size reporting and discovery for UEs in an IP network via the use of AT commands.